1. Field of the Invention
This invention relates to a duct type air conditioning system which employs a variable air volume (VAV) control capable of independently adjusting the temperature of each room.
2. Description of the Prior Art
Central air conditioning systems which distribute temperature adjusted air to each room via an air duct are widely employed in office buildings and the like because of their many advantages as compared with heat pump chiller-fan coil systems, decentralized packaged air conditioner systems, etc. A ducted central air conditioning system is capable of providing conditioned air with high quality since it may easily incorporate a humidifier and a high performance filter, and adapt to external or outdoor air ventilation and full heat exchange, and since each room which is to be air conditioned is provided with only a supply opening and a suction opening the room space can be used more effectively. Among the various types of central air conditioning systems, a variable air volume (VAV) control type which can be operated with saved energy is capable of controlling the temperature of each room having a different heating load independently, and it is also possible to stop the air conditioning of a room which is not used. Moreover, the operating cost can be reduced by varying the blower power depending on the required quantity of air, and it is also possible to minimize the size of the heat source taking the duty rate thereof into consideration.
There are several types of VAV systems. One is a throttle type unit in which the pressure within a duct, which changes depending on the degree of opening of a damper, is detected, and the blower capacity is controlled so that the detected pressure remains at a set value. When the load is decreased (even when the volume of blown air is decreased, the air temperature within the duct is controlled to be constant), the required capacity of the heat source is reduced, and at the same time the blower power is decreased.
Prior art VAV throttle type units are disclosed in Japanese Patent Publication No. 60-47497, and in FIG. 2.10(a) of the Refrigeration and Air Conditioning Handbook issued by the Japanese Association of Refrigeration.
FIG. 1 is a schematic diagram of an air conditioning system described in the above Handbook, wherein reference numeral 1 designates each of the four rooms to be air conditioned, reference numeral 2 designates an indoor unit disposed within the ceiling space of the building and composed of an air filter 3, a heat exchanger 4, and a blower 5, reference numeral 6 designates a main duct connected to an air supply opening of the indoor unit, 7 designates the four branch ducts for the rooms, 8 designates a VAV throttle unit inserted in a mid-portion of each branch duct, 9 designates a rotatable damper, 10 designates a supply opening provided in the end of each branch duct, 11 designates a suction opening provided at the bottom of each room door, 12 designates a suction opening provided in the ceiling of a corridor, 13 designates a duct connecting the ceiling opening 12 to the suction return of the unit 2, 14 designates room controllers (thermostats) each including a temperature sensor, 15 designates a temperature sensor disposed within the main duct 6, 16 designates a pressure sensor also disposed within the main duct, 17 designates a heat source device such as a heat pump or the like connected to the heat exchanger 4, 18 designates a control device for operating and controlling the heat source device, the blower 5, and the dampers 9, and 19 designates a main controller serving as an operating board to change over among modes including cooling, heating, stop, etc., and to set a program for room temperature.
In such a prior art air conditioning system, the degree of opening of each damper 9 is adjusted to a desired position in accordance with the difference between a temperature set by each room controller 14 and the sensed actual air temperature. Depending on the degree of opening of the dampers 9, the pressure within the main duct 6 is changed. This change is detected by the pressure sensor 16, and the capacity or output of the blower 5 is regulated o that a preset pressure is maintained. Further, since the outlet air temperature of the heat exchanger 4 is changed following a change in the volume of blown air, this temperature is detected by the temperature sensor 15, and the output of the heat source device 17 is controlled so that a preset air temperature is maintained. In this manner the air whose temperature is regulated to substantially a fixed degree is blown out from the supply openings 10 into the rooms 1 with a volume or at a rate corresponding to the magnitude of the heating load in each room. The conditioning supply air is returned through the suction openings 11 and the ceiling opening 12 to the indoor unit 2 via the suction duct 13 for recirculation.
The various control functions re carried out by the device 18 to achieve an optimum operation which satisfies energy saving and comfort conditions based on input signals from the main controller 19, the room controllers 14, temperature sensor 15, pressure sensor 16, and various other sensors (not shown) in the heat source device 17.
The control device 18 as shown in FIG. 2 includes, for example, a microprocessor, and its inputs/outputs are connected to each of the room controllers 14 by an I/O driver or the like. To each room controller 14, there are connected power supply lines and a plurality of signal transmission lines from the control device 18. Since there are four room controllers in the example shown, when two power supply lines and four signal transmission lines are needed for each room, installation work for a total of twenty-four lines (6 lines.times.4 rooms) is required for wiring and distribution to each of the rooms. Reference numeral 20 designates a heat source control circuit, and 21 designates a blower control circuit.
In such a prior art VAV system, the degree of opening of the dampers 9 is controlled based on the signals of the room controllers 14, and the temperature in each room is controlled accurately. At the same time, energy and cost are saved by closing the damper 9 of the first room 1 which is empty, and air conditioning is performed only for the rooms where it is required. In general, VAV air conditioning equipment for use in houses has not been widely accepted because of its high initial equipment and installation cost, even though its operating cost is comparatively low.